As shown in FIGS. 1A & 1B, the can, which is often made of tin, generally includes a can body 2, 2' having an operating top rim 21, 21' and a central top opening to be covered in an air-tight manner by a cover 1 having an operating top flange 11 for storing therein powdered milk, biscuit, cracker . . . or the like. Since top flange 11 is small and held extremely adjacent to can body 2, 2', it is always necessary to open the can with screwdriver, spoon, a pair of scissors . . . or the like which is, however, dangerous and/or inconvenient to the user troubled to find it out from somewhere. Certainly, it can be found there also is someone who is unwilling to be so troubled and thus does not want to airtightly utilize cover 1 which, certainly, is not a good way to use the can.